The Alabama-based company previously had exercised the 30-day payment grace period as it worked with its debt-holders to explore alternatives to recapitalise its balance sheet in light of what has been a challenging met coal pricing environment.

“The company will continue to engage in such discussions,” it said.

“Walter Energy noted it does not have a current liquidity issue, as it had approximately $US435 million of cash and investments as of March 31, 2015.

“It will continue to deliver high quality met coal to customers and meet its other obligations as it works with its debtholders to address the company's capital structure.”

The earnings and cash flow outlook for Walter Energy appear bleak and the company is running out of options to stay functional, a Seeking Alpha analyst said.

“In recent years, met coal demand has been slowing down while supply has been strong, which has created a glut in the met coal market and has kept prices weak,” the analyst said.

“Going forward, I do not foresee any noticeable improvement in met coal prices, therefore, the performance of US met coal miners like Walter Energy and Alpha Natural Resources is expected to remain challenging.”